Multi-targeting method and multi-targeting sensor device for locating short-range target objects in terms of distance and angle

ABSTRACT

A multi-targeting method for locating short-range target objects in terms of distance and angle. The method includes the following steps: a) a characteristic signal is emitted by a transmitting antenna of a first sensor element; b) the reflected characteristic signal is received by at least two adjacent reception antennae of the first sensor element; c) the difference in transit time of the reflected characteristic signal to the two adjacent reception antenna of the first sensor element is measured in order to determine the distance between the target objects and the first sensor element; and d) the phase differences of the characteristic signal between the two adjacent reception antenna of the first sensor element are measured in order to determine the angles between the target objects and the first sensor element. In addition, a device for implementing the above-mentioned method.

TECHNICAL AREA OF THE INVENTION

The present invention relates in general to a multitarget-capable methodand a multitarget-capable sensor device for distance and anglepositioning of close-range target objects. More specifically, thepresent invention relates to a multitarget-capable radar sensor devicefor distance and angle positioning of close-range target objects and amethod for operating such a multitarget-capable radar sensor device.

BACKGROUND INFORMATION

The position of target objects located at a great distance compared tothe dimensions of a measuring device may be determined usingconventional radar technology among other things. The distance anddirection (angle) of a target object to be detected must be determinedin this case. A narrow beam lobe of a radar is panned to determine thedirection. Antennas or antenna groups having a high directional effect,whose dimensions are multiples of the radar's wavelength, are needed togenerate the narrow beam lobe.

The above-described radar is disadvantageous in that it is relativelyexpensive and requires considerable space due to the large antennaapertures.

As an alternative, radar sensors delivering angle measurements viatriangulation to determine the position of a target object have beendeveloped in the related art.

However, considerably more than two sensor elements located at differentdistances must be used to prevent ghost targets and obtain unambiguousangle measurements. Ghost targets mean that after detecting thedistances of multiple targets using multiple sensor elements there aremultiple possible ways of combining the individual distance values todetermine the position of the target objects.

FIG. 1 shows such a problem of ghost target detection, where theambiguous evaluation of the distance information available from thesensor elements is shown for the case where two sensor elements 1 and 2are used. The ghost targets are located at the points of intersection ofthe arcs of circle drawn through the particular target objects to bedetected from sensor elements 1 and 2 (as centers). The number of targetobjects is thus doubled according to the example of FIG. 1.

In addition, it has been found disadvantageous in triangulation that theangular resolution is extremely inaccurate in the case of largedistances of the target objects compared to the distance of the sensorelements.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to avoid thedisadvantages of triangulation and provide a multitarget-capable methodand a multitarget-capable sensor device for distance and anglepositioning of close-range target objects where there is no risk ofghost target detection.

This object and other objects recited in the description that followsare achieved via a multitarget-capable method and a multitarget-capablesensor device for distance and angle positioning of close-range targetobjects according to the appended claims.

The multitarget-capable radar according to the present invention forproviding the distance and direction of multiple target objects includesat least one sensor element which emits a characteristic signal (e.g.,FMCW, pulse, or pseudo-noise), the characteristic signal beingevaluated, after reflection on the target objects to be positioned, bytwo or more receivers whose antennas are adjacent to one another. Thedistance between the antennas is preferably in the range of the sensorelements' wavelengths. In the evaluation, the distances to the targetobjects are obtained conventionally, it being possible to unambiguouslyassign only one phase difference between the signals received by thereceivers, corresponding to the direction of the target objects, to eachmeasured target object distance. Each sensor element of this type istherefore multitarget-capable despite the small antenna group of two ormore antennas, as long as only one target object is contained in eachdistance range.

According to a further particularly preferred aspect of the presentinvention, two or more sensor elements according to the presentinvention located at a distance from one another which is greater thanthe distance resolution of the sensor elements may be used to obtainunambiguous angle measurements for all target objects without exception.The sensor device is thus completely multitarget-capable, because thelimitation that each target object has a different distance to thesensor element always applies to two sensor elements. Only few sensorelements are needed, which have a simple design, because mechanicalpanning, large-aperture antennas, or many receivers are not needed.

According to a further aspect of the present invention, when multiplesensor elements are used, all signal paths between their transmittersand receivers may be used, whereby a plurality of reflection pointsrepresents the target object contours. This advantageously makes itpossible to recognize not only the direction and distance, but also thespatial shape of target objects.

In a further embodiment of the present invention, the beam lobes of thetransmitter antennas may also be panned to further increase unambiguity.In this case different antenna lobes may be used consecutively fortransmission and reception. For example, a maximum and a zero positionmay be directed alternately onto the target objects.

BRIEF DESCRIPTION OF THE DRAWING

Further features and advantages of the present invention, as well as thedesign and mode of operation of different embodiments of the presentinvention are described below with reference to the appended drawing.The appended drawing illustrates the present invention and, togetherwith the description, elucidates the principles of the invention,allowing those skilled in the art to implement and use the presentinvention.

FIG. 1 shows the problem of ghost target detection in a method of therelated art using triangulation for detecting the direction of a targetobject;

FIG. 2 shows a sensor element for determining, according to the presentinvention, the angle of incidence in the case of a single target object;

FIG. 3 shows the superposition of the waves from two differentdirections in a sensor element of FIG. 2;

FIG. 4A shows a sensor element according to the present invention havinga pulse generator for determining the angle of incidence in the case ofone target object or a plurality of target objects;

FIG. 4B shows a sensor element according to the present invention havinga PN generator for determining the angle of incidence in the case of onetarget object or a plurality of target objects;

FIG. 4C shows a signal response function (e.g., pulse response) plottedagainst the distance, the maxima of the signal response function beinglocated at the points of the target object distances;

FIG. 5 shows an additional embodiment of the present invention having asystem of three sensor elements for recognizing an elongated object anda punctiform object;

FIG. 6 shows another embodiment of the present invention having aplurality of sensor elements mounted on a vehicle, which are operated intransmission multiplex mode according to Table 1;

FIG. 7 shows the measurement of the angle to one or more target objects,a transmission lobe having a maximum in the panning angle directionbeing panned, and the lobe of the receiving antenna beingomnidirectional;

FIG. 8 shows the measurement of the angle to one or more target objects,a split transmission lobe having a minimum in the panning angledirection being panned, and the lobe of the receiving antenna beingomnidirectional;

FIG. 9 shows the measurement of the angle to one or more target objects,a transmission lobe having a maximum in the panning angle directionbeing panned, and the lobe of the receiving antenna also being pannedstepwise; and

FIG. 10 shows the measurement of the angle to one or more targetobjects, a split transmission lobe having a minimum in the panning angledirection being panned, and the split lobe of the receiving antenna alsobeing panned stepwise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 2, a sensor element 10 for determining, accordingto the present invention, angle of incidence ø (direction) is shown inthe case of a single target object (not shown). Sensor element 10 has atransmitting antenna II and at least two receiving antennas 1 and 2.Each of receiving antennas 1 and 2 is connected to a quadrature detector21, 22, which demodulates the particular signals U₁ and U₂ of thereceiving antennas into in-phase (I) and quadrature (Q) signals.Subsequently, the demodulated signals are subjected to an A/D conversionin the particular converters 31 and 31 and supplied, over bus 40, toprocessing unit 50, where angle of incidence ø of the wave reflected onthe single target object is computed using the phase difference betweenthe receiving antennas on the basis of the following formula:${\sin\quad\varphi} = {\frac{2}{\pi}{\arctan( {j\frac{{\underset{\_}{u}}_{1} - {\underset{\_}{u}}_{2}}{{\underset{\_}{u}}_{1} + {\underset{\_}{u}}_{2}}} )}}$

Further details for demodulation using a quadrature detector are knownto those skilled in the art and described in U.S. Pat. No. 6,184,830(Owens) or U.S. Pat. No. 5,541,608 (Murphy), and are not repeated here.

If a plurality of target objects is to be detected, it is no longerpossible to make an unambiguous angle measurement using only tworeceiving antennas according to the above-described principle and theabove formula. FIG. 3 shows this problem, illustrating the superpositionof the waves from two different directions at a single sensor elementdesigned according to FIG. 2.

From the superposition of the waves reflected from target objects 1 and2, an angle computed from the mean of the weighted angles of incidenceα₁, and α₂ results from the phase difference between the adjacentreceiving antennas. It is no longer possible to determine these anglesof incidence α₁ and α₂ individually from this information. An additionalreceiving antenna is needed for resolving these angles of incidenceseparately. The number of resolvable angle ranges, i.e., the angularresolution, is determined by the number of receiving antennas.Therefore, for a multitarget-capable radar system a group antenna havinga very narrow pannable lobe must be used if a mechanically pannableantenna is to be avoided. The aperture of the group antenna is thereforelarge compared to the wavelength and the circuit is consequently moreexpensive, because a dedicated receiver or an RF switch is needed foreach receiving antenna.

In the system according to the present invention, the direction of thetarget objects is determined by additionally measuring the differencesin propagation time between the adjacent receiving antennas in smallantenna arrays.

As shown in FIGS. 4A and 4B, which show embodiments of the presentinvention having a pulse generator and a PN generator, respectively, thesystem according to the present invention has a sensor element 10, whichdetects the distances of a plurality of target objects (not shown) bymeasuring the propagation times, and detects the phase differencebetween two adjacent receiving antennas 1 and 2 separately for eachdetected distance α₁, and α₂; an associated angle α₁, and α₂ is thencomputed for each distance from the phase difference. Ambiguous anglemeasurements are only possible in those cases where two or more targetobjects have the same distance to the one sensor element.

The transmitter sends a time-variable signal to the surroundings via apulse generator 60 or a PN generator 60′ via transmitting antenna 11 andthis signal is scattered back by multiple target objects. Theback-scattered signal is received at receiving antennas 1 and 2positioned preferably at a distance of half-wavelength, for example, andtransported into the base band by the circuit shown, similar to thecircuit of FIG. 2, by magnitude and phase. In each of the two receivepaths, a complex signal response/distance function is formed, the phaseof the complex function values corresponding to the phase of thereceived signal. Thus, for example, a response/distance-from-the-sensorfunction is obtained from the pulse response in the case of a pulseradar or from the correlation function in the case of a PN (pseudo-noisecode) radar, the response/distance-from-the-sensor function havingmaximums at those distances from the sensor where there are reflectionpoints, i.e., target objects. The correlation preferably takes place viaa predefined delay, which is provided via the particular programmabledelay elements 61. The phase of the signal back-scattered by theparticular target object may be read at each of the maximums, becausethe phase has been transported through into the base band. By comparingthe response functions generated in the two receive paths, phasedifference Δφ of the signal back-scattered by each target object may bedetermined for this target object, i.e., for the corresponding maximum.This phase difference also exists between the receiving antennas. FIG.4C, which shows the signal response functions plotted against thedistance using the pulse response as an example, shows the maximums atwhich phase differences Δφ₁ and Δφ₂ of the reflected signals of targetobjects 1 and 2 are determined. As explained previously, the maximumsare located at the point of the target object distances. The responsefunction on the first receive path to and from the first target objectis illustrated using a solid line. The response function on the secondreceive path to and from the second target object is illustrated using adashed line.

A conclusion concerning the particular angle of incidence α₁ and α₂ maynow be drawn separately for each target object from the phase differencebetween the signals at the two receiving antennas by the principle ofretrodirective arrays.

For example, if a target object is at angle α₁ and a second targetobject is at angle α₂ to adjacent receiving antennas 1 and 2, angles ofincidence α₁ and α₂ of the wave reflected by the target object may becomputed from the phase difference between the receiving antennas usingthe corresponding formulas:

As FIG. 4C shows, among other things, the maximums coincide in the caseof two target objects located at the same or approximately the samedistance from the one sensor element, so that no unambiguous detectionof angles of incidence α₁ und α₂ is possible.

According to the present invention, in this case the use of two or moresensor elements installed at different locations is proposed. This thenproduces the unambiguity, because two or more target objects which havethe same distance to one of the sensor elements must have a differentdistance to the other sensor element(s).${\sin\quad\alpha_{1}} = {\frac{2}{\pi}{\arctan( {j\frac{{\underset{\_}{u}}_{11} - {\underset{\_}{u}}_{21}}{{\underset{\_}{u}}_{11} + {\underset{\_}{u}}_{21}}} )}}$${\sin\quad\alpha_{2}} = {\frac{2}{\pi}{\arctan( {j\frac{{\underset{\_}{u}}_{12} - {\underset{\_}{u}}_{22}}{{\underset{\_}{u}}_{12} + {\underset{\_}{u}}_{22}}} )}}$Therefore, if the angle of two target objects cannot be detected by onesensor element because the target objects are located in the samedistance cell, it is possible to determine the position of the targetobjects in each of the additional sensor elements, because the targetobjects are located in different distance cells with respect to thosesensor elements. In principle, two sensor elements are sufficient toposition all target objects in this way. Further sensor elements may,however, be used to increase the accuracy and the range of unambiguity,also advantageously providing assurance in the case where there is no orinsufficient reception at one of the sensor elements.

FIG. 5 shows the recognition of the contour line of an elongated targetobject (e.g., bumper) and a “punctiform” target object (e.g., lamppost)using three networked sensor elements 10, 10′, and 10″.

Angle recognition in each sensor element 10, 10′, and 10″ is necessaryto obtain an unambiguous determination of the position of the scatteringpoints and takes place in a manner similar to the previously describedembodiments of the present invention. The use of multiple sensorelements 10, 10′, and 10″ at different points results in no erroneousangle information being obtained when multiple scattering points havethe same distance to a sensor element. In addition, at least a number ofscatter points equal to the number of sensor elements is detectable onelongated target objects (such as bumpers, for example). The networkingof all sensor elements over their wireless paths results in at least anumber of scatter points equal to the number of possible paircombinations among all sensor elements being detected on elongatedtarget objects (such as bumpers, for example), as shown in FIG. 5. Afurther target object such as a lamppost, for example, may also besimultaneously detected by the sensors.

The measurement results of the networked sensor elements are analyzedvia suitable programming of the processing unit, which contains thephase and distance information of each of the sensor elements, and, forexample, in the case of ambiguity (no distance between the detectedmaximums) the unanalyzable information is filtered out and only theinformation of the sensor elements having a favorable position isanalyzed.

In the embodiment of FIG. 5 having a plurality of sensor elements, thesesensor elements, in the form of PN code sensors, may transmit andreceive simultaneously past one another, or in time multiplex asdescribed as an example in Table 1. TABLE 1

In one embodiment of the present invention, shown in FIG. 6, sensorelements A through H of Table 1, operated in time multiplex, may bemounted on a vehicle to cover all relevant detection directions.

An additional embodiment of the angle recognition using small antennagroups is now described with reference to FIGS. 7 through 10. In thisembodiment, different shapes of beam panning and the principle of smartantennas applied to positioning from different points of installationare used.

There is also a small group of transmitting antennas in the direction oftransmission, with each antenna or at least each subgroup beingcontrollable separately by amplitude and phase; antenna lobes ofdifferent types may thus be generated and panned. The multitude ofpossible antenna lobes results in higher angular resolution of thesystem because multiple types of transmitting antenna lobes are pannedconsecutively and the receiving lobes are panned simultaneously. Fourdegrees of freedom may thus be used to vary the type of anglemeasurement:

-   -   1. Shape of the transmitting antenna's lobe (e.g., with maximum        or minimum in the direction of the panning angle),    -   2. Shape of the receiving antenna lobe,    -   3. Panning angle of the transmitting antenna lobe, and    -   4. Panning angle of the receiving antenna lobe.

These four degrees of freedom are independent of one another. If theangle measurement is varied consecutively in all four degrees offreedom, the accuracy of the angle measurement is increased manifoldcompared to an angle measurement resulting from panning a single type oflobe. The existence of further synchronized sensor elements capable oftransmitting simultaneously in any combination may be considered a fifthdegree of freedom. The different points of installation of the sensorelements in space are therefore also used to increase the variability ofthe measurements.

A plurality of different angle measurements are thus obtained whichoverall provide much more reliable data regarding multitargetcapabilities and accuracy than a single conventional angle measurement.Some exemplary configurations, which illustrate the variations of thepresent invention with reference to the above-mentioned four degrees offreedom, are elucidated in the example below.

Example: system featuring transmitting antenna A and receiving antennaB: With reference to FIG. 7, a wide-lobe and therefore low-resolutionangle scan is first performed using an antenna lobe whose maximum is inthe direction of panning angle α. To improve the resolution in thismeasurement, the width of the antenna lobe could be reduced only byusing larger arrays. To save the expense of large arrays, the type ofthe measurements is varied here consecutively according to theabove-mentioned four degrees of freedom.

As FIG. 7 shows, in measurement 1, a transmission lobe having a maximumin the direction of the panning angle is panned, the lobe of thereceiving antenna being omnidirectional.

Transmission maximums or at least higher transmission values occur inmeasurement 1 for those panning angles α which are directed at targetobjects or scattering points on target objects.

In subsequent measurement 2, a split antenna lobe is panned, as shown inFIG. 8. As expected, minimums occur at panning angles α which aredirected at target objects or scattering points on target objects. Sincethe interference effects due to superposition of the back-scattering ofother target objects are different in this measurement from those ofmeasurement 1, the influence of the interference effects on themeasurement accuracy may be reduced by processing the results ofmeasurement 1 and measurement 2 together. A target object is thuspreferably in direction a if measurement 1 shows an increased value andmeasurement 2 shows a minimum at the same time.

If the receiving lobe is now panned in different variations as shown inFIGS. 9 and 10, the directions of the target objects are determined witha greater accuracy from the plurality of measurement results. Atransmission lobe having a maximum in the panning angle direction isthus panned, for example, in the measurement according to FIG. 9, thelobe of the receiving antenna also being panned stepwise. In FIG. 10,measurement 4 is made by panning a split transmission lobe with aminimum in the panning angle direction, the split lobe of the receivingantenna also being panned stepwise.

When features in the claims are provided with reference symbols, thesereference symbols are provided only for better understanding of theclaims. Therefore, such reference symbols represent no limitations ofthe scope of protection of such elements which are only marked with suchreference symbols as examples.

1-18. (canceled)
 19. A method for distance and angle positioning of aplurality of close-range target objects, the method comprising the stepsof: a) transmitting a characteristic signal using a transmitting antennaof a first sensor element; b) receiving the characteristic signalreflected from the plurality of target objects using at least twoadjacent receiving antennae of the first sensor element; c) measuringpropagation time differences of the reflected characteristic signal tothe at least two adjacent receiving antennas so as to a determinerespective distances of the target objects to the first sensor element;and d) determining an angle of incidence for each of the target objectsto the first sensor element, wherein the determining of the angle ofincidence includes measuring phase differences of the reflectedcharacteristic signal between the at least two adjacent receivingantennas, by subjecting each of the reflected characteristic signalsreceived by the receiving antennae to a correlation with the transmittedcharacteristic signal so as to determine a complex correlation functionthat uniquely associates the measured phase differences with a distance,drawing a conclusion regarding the angle of incidence for each of thetarget objects according to the principle of retrodirective arrays. 20.The method as recited in claim 19, further comprising the steps of: e)transmitting a second characteristic signal using a transmitting antennaof a second sensor element, the second sensor element disposed at adistance from the first sensor element; f) receiving the reflectedcharacteristic signal using at least two adjacent second receivingantennae of the second sensor element; g) measuring propagation timedifferences of the reflected characteristic signals to the at least twoadjacent second receiving antennae of the second sensor element so as todetermine respective distances of the target objects to the secondsensor element; and h) measuring phase differences of the reflectedcharacteristic signal between the two adjacent second receiving antennasto determine an angle of incidence of each of the target objects to thesecond sensor element.
 21. The method as recited in claim 20, whereinthe steps e) through h) are performed only when the propagation timedifferences measured in the first sensor element are approximately equalto zero.
 22. The method as recited in claim 19, wherein thecharacteristic signal is one of a FMCW pulse signal and a pseudo-noisesignal.
 23. The method as recited in claim 19, wherein the furthercomprising a second sensor element and a third sensor elementinterconnected with the first sensor elements.
 24. The method as recitedin claim 19, further comprising varying a characteristic of the firstsensor element, wherein the characteristic includes one of a shape of alobe of the transmitting antenna, a shape of a lobe of one of the atleast two receiving antennae, a panning angle of the transmittingantenna lobe, and a panning angle of the lobe of the one of the at leasttwo receiving antennae.
 25. The method as recited in claim 24, whereinthe shape of the lobe having a maximum or a minimum in the direction ofthe panning angle is varied.
 26. The method as recited in claim 20,wherein the distance between two sensor elements is greater than thedistance resolution of any of the sensor elements.
 27. The method asrecited in claim 19, wherein measurement of the propagation timedifferences of the reflected characteristic signals includes detectingmaximums of signal/response functions of the characteristic signal, andthe measuring of the phase differences includes measuring the phasedifferences at the particular maximums.
 28. A sensor device for distanceand angle positioning of a plurality of close-range target objects, thesensor device comprising: a first sensor element having a firsttransmitting antenna and at least two adjacent first receiving antennae,the first transmitting antenna being configured to transmit acharacteristic signal, and the at least two first adjacent receivingantennae being configured to receive the characteristic signal reflectedfrom the plurality of target objects; a measuring device configured tomeasure propagation time differences of the reflected characteristicsignal to the two adjacent first receiving antennas so as to determinerespective distances of each target object to the first sensor element;and a device configured to measure phase differences of the reflectedcharacteristic signal between the two adjacent receiving antennae so asto determine a respective angle of each target object to the firstsensor element; a correlator configured to subject each reflectedtransmission signal received by the first receiving antennae to acorrelation with the characteristic signal so as to determine a complexcorrelation function uniquely associating the obtained phase informationwith a distance; and a comparer unit configured to draw a conclusionwith regard to the respective angle of incidence for each target objectfrom the phase difference between the signals at the two receivingantennae according to the principle of retrodirective arrays.
 29. Thesensor device as recited claim 28, further comprising; a second sensorelement disposed at a distance from the first sensor element, the secondsensor element including a second transmitting antenna configured totransmit a second characteristic signal, at least two adjacent secondreceiving antennas configured to receive the reflected characteristicsignal; and a second measuring device to measure propagation timedifferences of the reflected characteristic signals between the twoadjacent second receiving antennae to determine respective distances ofeach of the target objects to the second sensor element; and a seconddevice configured to measure respective phase differences of thereflected characteristic signal between the two adjacent secondreceiving antennas so as to determine a respective angle of incidencesof each of the target objects to the second sensor element.
 30. Thesensor device as recited in claim 29, wherein the second deviceconfigured to measure phase differences is also configured to detectphase and propagation time differences with the aid of the second sensorelement where the propagation time differences measured in the firstsensor element are approximately or equal to zero.
 31. The sensor deviceas recited in claim 28, wherein the characteristic signal includes oneof an FMCW signal, a pulse signal, and a pseudo-noise signal.
 32. Thesensor device as recited in claim 28, further comprising a second sensorelement and a third sensor element interconnected with the first sensorelement.
 33. The sensor device as recited in claim 28, wherein thetransmitting and/or receiving antennae are designed to enable a varyingof at least one characteristic, the characteristic including at leastone of a shape of a lobe of the transmitting antenna a shape of a lobeof one of the receiving antenna, a panning angle of the transmittingantenna lobe, and a panning angle of one of he receiving antennae lobes.34. The method as recited in claim 33, wherein the shape of the lobehaving a maximum or a minimum in the direction of the panning anglecapable of being varied.
 35. The sensor device as recited in claim 29,wherein the distance between the first and second sensor elements isgreater than a distance resolution of any of the sensor elements. 36.The sensor device as recited in claim 29, wherein the device configuredto measure phase differences is also configured to measure propagationtime differences of the reflected characteristic signals using maximumsof signal/response functions of the characteristic signal, the phasedifferences being measured at the respective maximums.